In a UMTS (Universal Mobile Telecommunications System) network, for the purposes of further increasing data rates, providing low delay and so on, long-term evolution (LTE) has been standardized (see Non Patent Literature 1)
In LTE, as multi access schemes, OFDMA (Orthogonal Frequency Division Multiple Access) based system is adopted for downlink and SC-FDMA (Single Carrier Frequency Division Multiple Access) based system is adopted for uplink.
For the purpose of achieving further broadbandization and increased speed beyond ETC, successor systems to LTE referred to as, for example, “LTE-advanced” or “LTE enhancement” are under study and the specifications thereof have been drafted as Rel. 10/11.
Also, the system band of the LTE Rel. 10/11 system includes at least one component carrier (CC), where one CC constitutes one unit of the system band of the LTE system. A plurality of CCs are aggregated into a wide band, which is referred to as “carrier aggregation” (CA). In this description, CCs are also simply referred to as “cells.”
In another successor system to LTE, LTE Rel. 12, various scenarios are under study in which a plurality of cells use different frequency bands (carriers). When a plurality of radio base stations forming cells are substantially the same, above-described CA can be applied. On the other hand, when the radio base stations forming cells are completely different, dual connectivity (DC) may be applied.
Carrier aggregation (CA) may be called “Intra-eNB CA” and dual connectivity (DC) may be called “Inter-eNB CA”.
When DC is used, a user terminal is configured to allocate uplink control information (UCI) to an uplink control channel (PUCCH: Physical Uplink Control Channel) not only in the primary cell (PCell), but also in at least one secondary cell (SCell) and send feedback to the radio base stations.